JP2008184043A - Electric power steering device and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To lower the machining accurracy of a bearing support member and a rack housing by relaxing the control of a dimensional tolerance when an axial position is determined. <P>SOLUTION: This electric power steering device comprises a rack housing RH on a vehicle lower side and a gear housing GH on a vehicle upper side. A bearing support member BS is installed between these housings. In the gear housing GH and the bearing support member BS, the gear housing GH is held by press fitting after being heated at 60&deg;C for 15 minutes, and the gear housing GH and the rack housing RH are fastened to each other with bolts 50. By the design in which a gap is formed between the bearing support member BS and the rack housing RH, the control of the dimensional tolerance when the axial position is determined is relaxed, and the machining accuracy of the bearing support member BS and the rack housing RH can be lowered. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention detects a steering torque by a torque sensor, and transmits an auxiliary steering torque generated from an electric motor corresponding to the detected steering torque to an output shaft of the steering mechanism via a speed reduction mechanism. The present invention relates to a power steering device and a manufacturing method thereof.

  In an electric power steering apparatus using an electric motor as a power source, a steering torque applied to a steering wheel is detected by a torque sensor, and an auxiliary steering torque generated from the electric motor corresponding to the detected steering torque is detected from a speed reduction mechanism. This is transmitted to the output shaft of the steering mechanism via the power transmission mechanism.

  In the electric power steering apparatus equipped with a speed reduction mechanism using a worm and a worm wheel as the power transmission mechanism, the worm wheel meshes with the worm connected to the drive shaft of the electric motor. Is fitted to an output shaft connected to the.

  In Patent Document 1, which is a prior application by the present applicant, in order to be able to measure performance such as friction and assist torque in the speed reduction mechanism unit itself, it is divided into a gear housing and a rack housing, and joined and positioned by a bearing support member. Yes.

  The bearing support member is sandwiched and fixed between the gear housing and the rack housing so as not to move in the radial axial direction.

  FIG. 5 is a cross-sectional view of the pinion assist type electric power steering device disclosed in Patent Document 1. As shown in FIG.

  An output shaft 32 that is a pinion shaft is connected to a lower side of the pinion shaft 7 that is an input shaft 31 via a torsion bar 33. That is, the base end of the torsion bar 33 is press-fitted and fixed to the output shaft 32, and the torsion bar 33 extends inside the hollow input shaft 31, and the tip thereof is the end of the input shaft 31. It is fixed to the part by a fixing pin 34.

  A torque sensor unit 3 is provided on the vehicle front side of the input shaft 31. That is, a torque detection groove 35 of the torque sensor unit 3 is formed on the vehicle front side of the input shaft 31, and a sleeve 36 is disposed radially outward of the torque detection groove 35. . The sleeve 36 has a vehicle front side end portion fixed to a vehicle rear side end portion of the output shaft 32 by plastic deformation of a part of the end portion. A plurality of rectangular windows (not shown) are formed in the sleeve 36 so as to face the torque detection groove 35 of the input shaft 31 in the radial direction. A coil 37, a substrate, and the like are provided in the gear housing GH outside the rectangular window of the sleeve 36 in the radial direction.

  A worm wheel 39 is fitted and fixed to the output shaft 32. The worm wheel 39 meshes with a worm 38 connected to the drive shaft of the electric motor 23. The worm wheel 39 includes a metal core 39a fitted to the output shaft 32 and resin gear teeth 39b formed on the metal core 39a.

  Steering force generated when the driver steers a steering wheel (not shown) is transmitted to a steered wheel (not shown) via an input shaft 31, a torsion bar 33, an output shaft 32, and a rack and pinion type steering device. The Further, the rotational force of the electric motor 23 is transmitted to the output shaft 32 via the worm 38 and the worm wheel 39. By appropriately controlling the rotational force and the rotational direction of the electric motor 23, the output shaft Appropriate steering assist torque can be applied to 32.

  A speed reduction mechanism including the worm 38 and the worm wheel 39 is housed in a gear housing GH and a bearing support member BS fitted to the gear housing GH.

  The input shaft 31 is rotatably supported by a first bearing 41 interposed on the inner wall of the gear housing GH, and the output shaft 32 is rotatable by a second bearing 42 interposed on the inner wall of the bearing support member BS. I support it.

  The rack 44 of the rack shaft 22 (FIG. 2) meshes with the pinion 43 of the output shaft 32. The rack guide 45 is constantly pressed against the back surface of the rack 44 by an adjust cover 47 via a spring 46. As a result, the backlash at the meshing portion between the pinion 43 and the rack 44 is eliminated, and the rack 44 can be moved smoothly.

  The lower end of the pinion 43 of the output shaft 32 is rotatably supported by a needle bearing 48.

  The housing is composed of a rack housing RH on the vehicle lower side and a gear housing GH on the vehicle upper side, and a bearing support member BS is provided between the two.

  The bearing support member BS is fixed by being sandwiched between the gear housing GH and the rack housing RH so that the gear housing GH and the rack housing RH are immovable in the radial direction and the axial direction at the same time. .

The bearing support member BS functions as an inlay when a unit including the torque sensor unit 3, the speed reduction mechanisms 38 and 39, the input / output shafts 31 and 32, and the electric motor 23 is assembled to the rack unit, and the gear housing GH The rack housing RH is positioned in the radial direction. That is, the outer periphery of the bearing support member BS press-fitted into the gear housing GH protrudes from the mounting surface of the gear housing GH, and serves as a fitting reference to the rack housing RH.
Japanese Patent Application No. 2006-120915

  In Patent Document 1 described above, the bearing support member is sandwiched without a gap between the gear housing and the rack housing, so that it cannot move in the radial direction and the axial direction, and can receive a load acting in the radial direction and the axial direction. .

  On the other hand, since the bearing support member is sandwiched between the gear housing and the rack housing with no gap, it is important to manage the dimensional tolerance when determining the position in the axial direction. Processing accuracy is required.

  The present invention has been made in view of the circumstances as described above, and relaxes the management of dimensional tolerances when determining the position in the axial direction, thereby reducing the processing accuracy of the bearing support member and the rack housing. An object of the present invention is to provide an electric power steering apparatus and a method for manufacturing the same.

In order to achieve the above object, an electric power steering apparatus according to the present invention includes:
A speed reducing mechanism for decelerating and transmitting power from the electric motor;
A gear housing that houses the speed reduction mechanism;
A rack housing that is fixed to the gear housing and houses a pinion formed at an output shaft end of the speed reduction mechanism and a rack portion that meshes with the pinion;
A bearing support member for supporting the bearing of the output shaft,
It is characterized by being positioned in the gear housing in the axial direction and the radial direction by being press-fitted into the gear housing whose diameter has been expanded by utilizing thermal expansion.

  The electric power steering apparatus according to the present invention preferably includes an engagement structure for preventing radial and axial movement on the press-fitting surfaces of the bearing support member and the gear housing.

The manufacturing method of the electric power steering apparatus of the present invention is as follows.
A speed reducing mechanism for decelerating and transmitting power from the electric motor;
A gear housing that houses the speed reduction mechanism;
A rack housing that is fixed to the gear housing and houses a pinion formed at an output shaft end of the speed reduction mechanism and a rack portion that meshes with the pinion;
In order to manufacture an electric power steering apparatus comprising a bearing support member that is press-fitted into the gear housing and supports a bearing of the output shaft,
The bearing support member is positioned in the gear housing in the axial direction and the radial direction by press-fitting into the gear housing whose diameter has been expanded using thermal expansion.

  According to the present invention, the bearing support member is positioned and held in the axial direction and the radial direction by press fitting after the gear housing is heated and expanded. In addition, the bearing support member and the rack housing can be designed to have a gap in at least the axial direction, and the management of dimensional tolerances when determining the axial position is relaxed, and the processing accuracy of the bearing support member and the rack housing is reduced. Can be lowered.

  Furthermore, the joint surface between the gear housing and the bearing support member is an engagement structure such as a tapered surface or a concave-convex fitting portion, so that movement in the radial direction and the axial direction is prevented, and a load acting on the radial direction and the axial direction is prevented. Can receive.

  Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an entire steering mechanism incorporating an electric power steering apparatus according to an embodiment of the present invention. FIG. 2 is a partial sectional view in the axial direction of the periphery of the pinion assist type electric power steering apparatus according to the embodiment of the present invention.

  In FIG. 1, the steering wheel 1 is connected to an input shaft 2 a that constitutes the upper part of the steering shaft 2. The lower end of the input shaft 2 a is connected to the upper end of the lower shaft 2 b through the universal joint 4, and the lower end of the lower shaft 2 b is connected to the upper end of the pinion shaft 7 through the universal joint 5.

  A rack shaft 22 (FIG. 2) is inserted into the rack housing 8, and the rack shaft 22 is connected to the tie rods 9 and 10 at both ends thereof. The tie rods 9 and 10 are connected to a steering mechanism (not shown).

  The pinion shaft 7 is composed of an upper shaft 7 a and a lower shaft 7 b, and the upper shaft 7 a and the lower shaft 7 b are connected via the torque sensor unit 3.

  The torque sensor unit 3 detects a steering torque transmitted to the pinion shaft 7, and for example, a torsional angle displacement of a torsion bar (not shown) in which a steering torque is inserted between the upper shaft 7a and the lower shaft 7b. And the torsional angular displacement is detected magnetically or mechanically, and the operator steers the steering wheel 1 according to the size and direction of the torsion generated in the pinion shaft 7. A torque detection signal Tv composed of an analog voltage is output to the controller 13.

  For example, when the steering wheel 1 is in a neutral state, the torque sensor unit 3 outputs a predetermined neutral voltage as the torque detection signal Tv. When the voltage that increases from the neutral voltage according to the steering torque is counterclockwise, a voltage that decreases from the neutral voltage according to the steering torque at that time is output.

  A pinion 43 (FIG. 3) is connected to the lower end of the pinion shaft 7, and the pinion 43 meshes with the rack teeth of the rack shaft 22 (FIG. 2). The pinion shaft 7 is connected to the rotating shaft of the electric motor 23 through, for example, a worm gear mechanism.

  A controller 13 is provided to drive and control the electric motor 23 and control the steering assist force to the steering system. The controller 13 is operated by being supplied with power from a vehicle-mounted battery 16. The negative electrode of the battery 16 is grounded, and its positive electrode is connected to the controller 13 via an ignition switch 14 and a fuse 15a for starting the engine, and directly connected to the controller 13 via a fuse 15b. The power supplied via 15b is used for memory backup, for example.

  The controller 13 controls driving of the electric motor 23 based on a torque detection signal Tv from the torque sensor unit 3 and a vehicle speed detection signal Vp from a vehicle speed sensor 17 disposed on an output shaft of a transmission (not shown), for example. Can do.

  FIG. 3 is an enlarged cross-sectional view of a power assist mechanism portion of a pinion assist type electric power steering apparatus according to an embodiment of the present invention.

  An output shaft 32 that is a pinion shaft is connected to the lower side of the pinion shaft 7 that is the input shaft 31. The base end of the torsion bar 33 is press-fitted and fixed to the output shaft 32, and the torsion bar 33 extends inside the hollow input shaft 31, and the tip thereof is at the end of the input shaft 31. It is fixed by a fixing pin 34.

  A torque sensor unit 3 is provided on the vehicle front side of the input shaft 31. That is, a torque detection groove 35 of the torque sensor unit 3 is formed on the vehicle front side of the input shaft 31, and a sleeve 36 is disposed radially outward of the torque detection groove 35. . The sleeve 36 has a vehicle front side end portion fixed to a vehicle rear side end portion of the output shaft 32 by plastic deformation of a part of the end portion. A plurality of rectangular windows (not shown) are formed in the sleeve 36 so as to face the torque detection groove 35 of the input shaft 31 in the radial direction. A coil 37, a substrate, and the like are provided in the gear housing GH outside the rectangular window of the sleeve 36 in the radial direction.

  A worm wheel 39 is fitted to the output shaft 32. The worm wheel 39 meshes with a worm 38 connected to the drive shaft of the electric motor 23. The worm wheel 39 includes a core metal 39a fitted to the output shaft 32 and resin gear teeth 39b formed on the core metal 39a.

  Steering force generated when the driver steers a steering wheel (not shown) is transmitted to a steered wheel (not shown) via an input shaft 31, a torsion bar 33, an output shaft 32, and a rack and pinion type steering device. The Further, the rotational force of the electric motor 23 is transmitted to the output shaft 32 via the worm 38 and the worm wheel 39, and the output is controlled by appropriately controlling the rotational force and the rotational direction of the electric motor 23. An appropriate steering assist torque can be applied to the shaft 32.

  The speed reduction mechanism including the worm 38 and the worm wheel 39 is housed inside the gear housing GH and the bearing support member BS press-fitted into the gear housing GH as will be described in detail later.

  The input shaft 31 is rotatably supported by a first bearing 41 interposed on the inner wall of the gear housing GH, and the output shaft 32 is supported by a second bearing 42 interposed and fixed on the inner wall of the bearing support member BS. It is rotatably supported. That is, the bearing support member BS is supported by the gear housing GH so as not to be axially displaceable and rotatable. The second bearing 42 is preferably a four-point contact bearing.

  In the present embodiment, the gear housing GH on the upper side of the vehicle constitutes a housing together with the rack housing RH on the lower side of the vehicle.

  The outer periphery of the bearing support member BS is processed into a cylindrical shape, and the gear housing GH is positioned in the axial direction and the radial direction by being press-fitted and fixed after heating the gear housing GH at 60 ° C. for 15 minutes, and is held by the gear housing GH.

  The rack housing RH is fastened to the gear housing GH with bolts 50, and a gap is provided at least in the axial direction between the rack housing RH and the bearing support member BS.

  With such a structure, the speed reduction mechanism including the pinion 43 can measure performance such as friction and assist torque by itself without attaching the rack housing RH to the gear housing GH. In other words, the torque sensor unit 3, the speed reduction unit, the input / output shafts 31, 32, and the electric motor 23 can perform performance measurement in an integrally configured unit state. And the yield is improved.

  The rack 44 of the rack shaft 22 (FIG. 2) meshes with the pinion 43 of the output shaft 32. The rack guide 45 is provided in the rack housing RH, and is constantly pressed against the back surface of the rack 44 by an adjust cover 47 via a spring 46. As a result, the backlash at the meshing portion between the pinion 43 and the rack 44 is eliminated, and the rack 44 can be moved smoothly.

  The lower end of the pinion 43 of the output shaft 32 is rotatably supported by a needle bearing 48.

  The gear housing GH and the rack housing RH are sealed in the axial direction by a seal member 51. The seal member 51 is preferably an O-ring. Moreover, the 2nd bearing 42 which supports the output shaft 32 is a bearing with a seal | sticker which has airtightness. The first bearing 41 is also a sealed bearing having airtightness.

  According to this embodiment, the bearing support member BS and the rack housing RH are designed to have a gap at least in the axial direction, and management of dimensional tolerance when determining the position in the axial direction is eased. The processing accuracy of the member BS and the rack housing RH can be lowered.

  FIGS. 4A and 4B are enlarged cross-sectional views of an elliptical part surrounded by reference numeral IV in FIG. 3 according to a modification of the embodiment of the present invention.

  In the modification of FIG. 4A, the press-fitting surface (joint surface) of the gear housing GH and the bearing support member BS is a tapered surface 60, which is an engagement structure that prevents movement in the radial direction and the axial direction.

  The taper surface 60 can prevent the radial and axial movements and receive a load acting in the radial and axial directions.

  In the modified example of FIG. 4B, an engagement structure 61 is provided on the press-fitting surface (joint surface) of the gear housing GH and the bearing support member BS to prevent movement in the radial direction and the axial direction. It is said.

  By this engagement structure, movement in the radial direction and the axial direction can be prevented and a load acting in the radial direction and the axial direction can be received.

  In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation is possible.

1 is a schematic configuration diagram showing an entire steering mechanism incorporating an electric power steering apparatus according to an embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial axial sectional view of a periphery of a pinion assist type electric power steering apparatus according to an embodiment of the present invention. 1 is a cross-sectional view of a pinion assist type electric power steering apparatus according to an embodiment of the present invention. (A) and (b) are the expanded sectional views of the ellipse part enclosed by the code | symbol IV of FIG. 3, respectively, concerning the modification of embodiment of this invention. FIG. 6 is a cross-sectional view of a pinion assist type electric power steering device disclosed in Patent Document 1 with a rack housing mounted.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 8 Rack housing 22 Rack shaft 23 Electric motor 31 Input shaft 32 Output shaft 33 Torsion bar 38 Worm 39 Worm wheel 41 1st bearing 42 2nd bearing 43 Pinion 44 Rack 45 Rack guide 60 Tapered surface 61 Concavity and convexity fitting Joint part BS Bearing support member GH Gear housing RH Rack housing

Claims (3)

A speed reducing mechanism for decelerating and transmitting power from the electric motor;
A gear housing that houses the speed reduction mechanism;
A rack housing that is fixed to the gear housing and houses a pinion formed at an output shaft end of the speed reduction mechanism and a rack portion that meshes with the pinion;
A bearing support member for supporting the bearing of the output shaft,
An electric power steering apparatus characterized by being axially and radially positioned in the gear housing by being press-fitted into the gear housing whose diameter has been expanded by utilizing thermal expansion.   The electric power steering apparatus according to claim 1, wherein an engagement structure for preventing radial and axial movement is provided on a press-fitting surface of the bearing support member and the gear housing. A speed reducing mechanism for decelerating and transmitting power from the electric motor;
A gear housing that houses the speed reduction mechanism;
A rack housing that is fixed to the gear housing and houses a pinion formed at an output shaft end of the speed reduction mechanism and a rack portion that meshes with the pinion;
In order to manufacture an electric power steering device comprising a bearing support member that is press-fitted into the gear housing and supports a bearing of the output shaft,
A method of manufacturing an electric power steering apparatus, wherein the bearing support member is positioned in the gear housing in an axial direction and a radial direction by press-fitting into the gear housing whose diameter has been expanded using thermal expansion.

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